On Monday 16 July 2012 00:07:18 Peter C. Wallace did opine: > > Sure there is Jon. Timestamp the last 4 edges so you can develop an > > average speed over the total time period of those 4 stamps. Then add > > the last few digits for the position it is expected to be at the > > servo threads time. The only thing to complicate that would be a > > motion reversal within that 4 sample period. > > > > Or maybe I don't fully appreciate the problem. No explanation offered > > so far seems to explain why the encoders rps output, at a mechanical > > speed of 20 rps, has +- 3.xxx or more from the 20 its actually doing, > > flickering in the halmeter output. And this 'noise' does not seem to > > be all that much effected by the actual speed regardless of the speed > > as long as its over about 1 rps. > > > > Cheers, Gene > > Thats an awful lot of jitter (>15 %). I certainly dont see that with our > hardware that timestamps the encoder edges in conjunction with the > driver doing a counts/time_between_counts calculation of estimated > velocity. The software velocity estimation works the same as the > hardware AFAIK, so should have reasonably good jitter performance. > > So there are a couple of possibilities I see > > 1. Are you use the encoder components velocity output? > > 2. Is this wired to the PID comps feedback-deriv input? > > 3. Do you actually have a good signal from the encoder? > (things like HF tortional vibrations can play hell with velocity > estimation by causing apparent reversals at low speeds) > > Note that Scott Hasse in his using the encoder counter for a A-D scheme > with a V-F thought there was a problem with the encoder comp but found > out jitter in his signal was the problem, and that the encoder comp > performed as well as it could given the jitter and resolution of the > basethread timestamp > > > http://www.mail-archive.com/emc-users@lists.sourceforge.net/msg37885.htm > l I'll look at that tomorrow, after I get my .hal file made available. > > Can you connect a signal generator to the encoder comp and "bifurcate" > the problem? For that I would have to build a generator in order to send the proper quadrature. > Peter Wallace > Mesa Electronics > Thanks Peter.
Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! I'll pretend to trust you if you'll pretend to trust me. ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
